Question

Dada a sequencia (2,7,12,17) determine S9​

Answer 1

$> resolucao \\ \\ \geqslant progressao \: aritmetica \\ \\ > \: a \: razao \: da \: pa \\ \\ r = a2 - a1 \\ r = 7 - 2 \\ r = 5 \\ \\ \\ > \: o \: 9 \: termo \: da \: pa \\ \\ an = a1 + (n - 1)r \\ an = 2 + (9 - 1)5 \\ an = 2 + 8 \times 5 \\ an = 2 + 40 \\ an = 42 \\ \\ \\ \geqslant \: a \: soma \: dos \: 9 \: termos \: da \: pa \\ \\ \\ sn = \frac{(a1 + an)n}{2} \\ \\ sn = \frac{(2 + 42)9}{2} \\ \\ sn = \frac{44 \times 9}{2} \\ \\ sn = 22 \times 9 \\ \\ sn = 198 \\ \\ \\ > < > < > < > < > < > < > < > < > >$